The present invention relates to processing systems and methods for automatically determining predefined viewing directions of a heart from medical imaging data.
The standard views for the display of cardiac-related imagery are defined by the American Heart Association. These views include the short axis view, the vertical long axis view, and the horizontal long axis view. With reference to FIG. 1, the standard views may be defined in relation to the left ventricle 12 and right ventricle 14 of a heart 10, and include a short axis view (SA), a vertical long axis view (VLA) and a horizontal long axis view (HLA). For orientation reference FIG. 2 provides a schematic view of the heart and FIG. 3 provides a view of an image slice with right and left ventricles.
The short axis view is orthogonal to the long axis of the left ventricle, with the long axis going through the center of the image. The short axis cuts the long axis in the middle of the axis, and so the image is approximately centered on the center of the left ventricle. The viewing direction is from the cardiac apex towards the base of the left ventricle, with the top-side of the image pointing towards the anterior of the patient.
The vertical long axis view (VLA) is orthogonal to both the short axis view and the horizontal long axis view. For VLA views, the long axis of the left ventricle is parallel with the row vector of the, and goes through the center of the image (i.e. the long axis is a horizontal line dividing the image plane into upper and lower halves). The center of the image is aligned with the middle of the long axis of the left ventricle, with the viewing direction from right to left, and the top-side of the image pointing towards the anterior of the patient.
The horizontal long axis view (HLA) is orthogonal to both the short axis view and the vertical long axis view. For HLA views, the long axis of the left ventricle is parallel with the column vector of the image, and goes through the center of the image (i.e. the long axis is a vertical line dividing the image plane into left and right halves). The center of the image is aligned with the middle of the long axis of the left ventricle, with the viewing direction basically from the posterior to the anterior of the patient.
Much of the prior work has focused on scan planning for magnetic resonance imaging (MRI). Most cardiac MRI studies are two-dimensional (2D) in nature. Several 2D scout images are acquired to visualize the thorax and heart anatomy, and then a set of parallel 2D scans is done oriented with the short-axis of the heart. One or two long axis 2D images may also be scanned. Automating the process of planning this type of cardiac MRI study has been investigated. Lelieveldt et al., in an article entitled “Automated observer-independent acquisition of cardiac short-axis MR images: a pilot study”, in Radiology, 221(2), pages 537-542 (2001), automate planning for only the short-axis view. The work of Jackson et al., disclosed in an article entitled “Automatic Planning of the Acquisition of Cardiac MR Images”, in MICCAI, September 2003, pages 541-548, includes automatic planning of the long-axis views. Lelieveldt et al. use a template matching scheme for the entire thorax using fuzzy implicit surfaces on 2D images aligned with the axes of the scanner. The template includes a definition of the likely cardiac short-axis orientation. This is computationally expensive and assumes a fixed field of view. Jackson et al. use an Expectation-Maximization (EM) algorithm to segment the chambers of the heart in a stack of 2D scans that are taken at an orientation found to be a good approximation to the short axis in fifty adult patients. EM algorithms are also computationally expensive. A line is then fit through the centroids found for the left ventricle in each 2D image to determine the left ventricle long-axis. The HLA is defined at an orientation through the left ventricle long axis and the average of the points on the right ventricle farthest from the left ventricle.
In U.S. patent application Ser. No. 10/852,834 by T. O'Donnell and B. Cowan, filed May 25, 2004, and entitled “Automatic Optimal View Determination for Cardiac Acquisitions,” incorporated herein by reference, sampling the heart and chest in axial, sagittal, and coronal images and then using a pre-existing segmentation algorithm (such as the segmentation algorithm disclosed by M. P. Jolly in “Combining edge, region, and shape information to segment the left ventricle in cardiac MR images,” MICCAI, September 2001, pages 482-490) to find the borders of the left ventricle is disclosed. An ellipsoid is fit to these borders, and the long-axis of the ellipse is taken as a first approximation to the long-axis of the left ventricle. The direction of the HLA is determined as an orientation through the left ventricle long axis and the direction of the right ventricle relative to the left ventricle. The VLA is defined as being orthogonal to the SA and the HLA. These estimates can be refined by evaluating scans taken oriented with the estimated SA, HLA, VLA.
Despite the availability of these algorithms, it is nevertheless desirable to provide yet more accurate means of automatically estimating the SA, HLA, and VLA views from volumetric data.